Ronney Jenkins can not be sure whether chronic traumatic encephalopathy is clawing through his brain tissue right now , but he suspects that it is .

After all , he fits an emerging portrait of people diagnosed with the disease : a former professional football player who took lots of hits to the head -- a couple knocked him out -- and a life off the field that has begun to unravel .

`` My mood has changed , '' said Jenkins , 36 , a soft-spoken former running back who played for several teams , including the San Diego Chargers . `` Sometimes I think I 'm going crazy . ''

Jenkins began to suspect CTE several years ago when an uncharacteristic dark mood and , occasionally , deep anger began to bubble up at unexpected times .

`` I 'd be talking to a cousin of mine , disagree with him , and I 'd just want to do something to him , '' Jenkins said . `` I do n't know why I had those thoughts , but I wanted to hurt him . ''

Jenkins can not shake the feeling that these and other symptoms he has add up to CTE , but he will never be sure . The only way to diagnose CTE is after death -- by analyzing brain tissue and finding microscopic clumps of an abnormal protein called tau .

`` The problem is , people are diagnosing CTE clinically all over the place , '' said Robert Stern , professor of neurology and neurosurgery at Boston University School of Medicine . `` There is no framework to make that diagnosis while someone is alive . ''

Stern and his colleagues want to change that . He is co-author of a new study that is beginning to describe what the disease looks like during life .

The study , published Wednesday in the journal Neurology , suggests that when CTE symptoms emerge at a young age , players more often exhibit behavioral and mood problems , whereas symptoms that begin later in life tend to show up as memory and thinking problems .

Family members and loved ones of 36 athletes -- 29 football players , three professional hockey players , one professional wrestler and three boxers diagnosed with CTE after they died -- were quizzed about , among other things , the nature of the players ' CTE symptoms and when they appeared .

A tale of two former NFL players -- and their brains

According to those family reports , 11 players in the group first struggled with memory and decision-making , at an average age of 69 .

Twenty-two players first exhibited mood and behavior problems like depression and hopelessness or violent , explosive behavior . Those players tended to be younger when they died , an average age of 51 .

Three players did not display any symptoms before being diagnosed with CTE .

It is too early in the research to know why some symptoms crop up early and others later -- and why the symptoms seem to diverge , or not show up at all , depending on the player . One theory among scientists is that where and how the damage manifests in the brain matters .

For example , tau , which tends to be peppered in particular areas of the brains of people diagnosed with CTE , could damage brain tissue at different stages of the disease , depending on the person .

`` There is no specific order of changes in CTE ; it 's on a case-by-case basis , '' said Stern , who is also the co-founder of the Center for the Study of Traumatic Encephalopathy . `` It could be that some people have more initial changes to -LRB- brain -RRB- areas that are more responsible for mood and aggression and impulse control . ''

Symptoms could also be explained by other changes in the brain , associated with repetitive brain trauma , that have nothing to do with tau or CTE .

Junior Seau had brain disease that comes from hits to head

`` This disease remains somewhat mysterious in terms of exactly what its causes are and how it 's expressed , '' said Dr. Julian Bailes , co-director of the NorthShore Neurological Institute and a CTE researcher , who was not involved in the current study .

But Bailes says this study , though small and not generalizable for all cases of CTE , adds to current knowledge about the disease .

For example , the data did reveal other interesting patterns , particularly related to genetics .

The study participants with CTE were more likely than people without the disease to express the APOE gene , which is associated with slower recovery and worse cognition after traumatic brain injury ; it 's also associated with later development of Alzheimer 's disease .

Stern and his colleagues know that their study sample is skewed : People who tend to donate a loved one 's brain to be studied for CTE also tend to suspect a problem . And there is no formula for how many hits -LRB- or what type of hits -RRB- tip the balance toward symptomatic disease . There has also been no examination of what role things like steroids or body weight may play .

Even with those caveats , Stern is confident that `` eventually , clinicians will have the ability to diagnose the disease during life . ''

In the meantime , former players like Jenkins are left in a fight against time and the progression of whatever brain disease their concussions may have wrought .

`` I 'm paying attention to things more , '' he said , `` and I 'm more worried about my health . ''

In the meantime , researchers of many disciplines are scrambling to define a disease that 's definition is elusive at best .

`` For perspective , Alzheimer 's disease was first described in the first decades of the 1900s , and we still do n't have the ability to diagnose it definitively during life , '' Stern said . `` It still ca n't be cured , prevented or even slowed down . ''

Both Jenkins and Stern hope that for CTE , it will not be that long .

NFL Players Association , Harvard planning $ 100 million study

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CTE has been seen in brains of athletes who have taken a lot of hits to the head

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CTE can be diagnosed only after death , but a new study begins to describe symptoms

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Athletes with the disease exhibit behavioral and mood problems , as well as memory issues